# This file is dual licensed under the terms of the Apache License, Version
# 2.0, and the BSD License. See the LICENSE file in the root of this repository
# for complete details.
import abc
import typing
from cryptography import utils
from cryptography.exceptions import AlreadyFinalized
from cryptography.hazmat.bindings._padding import lib
[docs]class PaddingContext(metaclass=abc.ABCMeta):
[docs] @abc.abstractmethod
def update(self, data: bytes) -> bytes:
"""
Pads the provided bytes and returns any available data as bytes.
"""
[docs] @abc.abstractmethod
def finalize(self) -> bytes:
"""
Finalize the padding, returns bytes.
"""
def _byte_padding_check(block_size: int) -> None:
if not (0 <= block_size <= 2040):
raise ValueError("block_size must be in range(0, 2041).")
if block_size % 8 != 0:
raise ValueError("block_size must be a multiple of 8.")
def _byte_padding_update(
buffer_: typing.Optional[bytes], data: bytes, block_size: int
) -> typing.Tuple[bytes, bytes]:
if buffer_ is None:
raise AlreadyFinalized("Context was already finalized.")
utils._check_byteslike("data", data)
buffer_ += bytes(data)
finished_blocks = len(buffer_) // (block_size // 8)
result = buffer_[: finished_blocks * (block_size // 8)]
buffer_ = buffer_[finished_blocks * (block_size // 8) :]
return buffer_, result
def _byte_padding_pad(
buffer_: typing.Optional[bytes],
block_size: int,
paddingfn: typing.Callable[[int], bytes],
) -> bytes:
if buffer_ is None:
raise AlreadyFinalized("Context was already finalized.")
pad_size = block_size // 8 - len(buffer_)
return buffer_ + paddingfn(pad_size)
def _byte_unpadding_update(
buffer_: typing.Optional[bytes], data: bytes, block_size: int
) -> typing.Tuple[bytes, bytes]:
if buffer_ is None:
raise AlreadyFinalized("Context was already finalized.")
utils._check_byteslike("data", data)
buffer_ += bytes(data)
finished_blocks = max(len(buffer_) // (block_size // 8) - 1, 0)
result = buffer_[: finished_blocks * (block_size // 8)]
buffer_ = buffer_[finished_blocks * (block_size // 8) :]
return buffer_, result
def _byte_unpadding_check(
buffer_: typing.Optional[bytes],
block_size: int,
checkfn: typing.Callable[[bytes, int], int],
) -> bytes:
if buffer_ is None:
raise AlreadyFinalized("Context was already finalized.")
if len(buffer_) != block_size // 8:
raise ValueError("Invalid padding bytes.")
valid = checkfn(buffer_, block_size // 8)
if not valid:
raise ValueError("Invalid padding bytes.")
pad_size = buffer_[-1]
return buffer_[:-pad_size]
[docs]class PKCS7(object):
def __init__(self, block_size: int):
_byte_padding_check(block_size)
self.block_size = block_size
[docs] def padder(self):
return _PKCS7PaddingContext(self.block_size)
[docs] def unpadder(self):
return _PKCS7UnpaddingContext(self.block_size)
class _PKCS7PaddingContext(PaddingContext):
_buffer: typing.Optional[bytes]
def __init__(self, block_size: int):
self.block_size = block_size
# TODO: more copies than necessary, we should use zero-buffer (#193)
self._buffer = b""
def update(self, data: bytes) -> bytes:
self._buffer, result = _byte_padding_update(
self._buffer, data, self.block_size
)
return result
def _padding(self, size: int) -> bytes:
return bytes([size]) * size
def finalize(self) -> bytes:
result = _byte_padding_pad(
self._buffer, self.block_size, self._padding
)
self._buffer = None
return result
class _PKCS7UnpaddingContext(PaddingContext):
_buffer: typing.Optional[bytes]
def __init__(self, block_size: int):
self.block_size = block_size
# TODO: more copies than necessary, we should use zero-buffer (#193)
self._buffer = b""
def update(self, data: bytes) -> bytes:
self._buffer, result = _byte_unpadding_update(
self._buffer, data, self.block_size
)
return result
def finalize(self) -> bytes:
result = _byte_unpadding_check(
self._buffer, self.block_size, lib.Cryptography_check_pkcs7_padding
)
self._buffer = None
return result
[docs]class ANSIX923(object):
def __init__(self, block_size: int):
_byte_padding_check(block_size)
self.block_size = block_size
[docs] def padder(self) -> PaddingContext:
return _ANSIX923PaddingContext(self.block_size)
[docs] def unpadder(self) -> PaddingContext:
return _ANSIX923UnpaddingContext(self.block_size)
class _ANSIX923PaddingContext(PaddingContext):
_buffer: typing.Optional[bytes]
def __init__(self, block_size: int):
self.block_size = block_size
# TODO: more copies than necessary, we should use zero-buffer (#193)
self._buffer = b""
def update(self, data: bytes) -> bytes:
self._buffer, result = _byte_padding_update(
self._buffer, data, self.block_size
)
return result
def _padding(self, size: int) -> bytes:
return bytes([0]) * (size - 1) + bytes([size])
def finalize(self) -> bytes:
result = _byte_padding_pad(
self._buffer, self.block_size, self._padding
)
self._buffer = None
return result
class _ANSIX923UnpaddingContext(PaddingContext):
_buffer: typing.Optional[bytes]
def __init__(self, block_size: int):
self.block_size = block_size
# TODO: more copies than necessary, we should use zero-buffer (#193)
self._buffer = b""
def update(self, data: bytes) -> bytes:
self._buffer, result = _byte_unpadding_update(
self._buffer, data, self.block_size
)
return result
def finalize(self) -> bytes:
result = _byte_unpadding_check(
self._buffer,
self.block_size,
lib.Cryptography_check_ansix923_padding,
)
self._buffer = None
return result